Searching For a Motor To Drive Our DIY EV

Now that I’ve purchased a car to convert to electrical power, the next big step is finding an electric motor.

Everything I’ve learned during my crash course in EV conversions suggests the most difficult part of the job will be mating an electric motor to the the four-speed transmission in the 1967 VW Beetle I’m converting. My plan is get a motor, get someone to help me install it and then get the car to my garage to do the rest of the work.

So, what kind of motor am I using?

Insert motor here. The soot is from an engine fire the previous owner had.

Most do-it-yourselfers use large DC series wound motors. If you’ve read my previous posts, you know that I’m just an average Joe. I don’t fully understand what “series wound” means, but I do know such motors provide buckets of torque at low speed and they’re great for heavy loads. That’s why you often find them in heavy industrial equipment like forklifts. DC motors are typically brushed motor designs and have the benefit of being simple, cheap (a relative term) and easy to maintain.

They do have some downsides, though. The brushes require periodic, though infrequent, replacement. Most DC motors are limited to around 5,000 RPM, which is why you’ve got to bolt them to your car’s transmission. AC motors, on the other hand, can spin at higher RPM, negating the need for a complex gearbox. The Tesla Roadster, for example, uses an AC motor mated to a single-speed gearbox. DC motors also are slightly less efficient than AC motors, but the biggest downside is most DC motors are not capable of regenerative braking.

When I began my research I was surprised to find most people doing conversions aren’t using regenerative braking, which sends some of the kinetic energy of braking back to the batteries. AC motors provide regenerating capabilities almost by default, but the motors and equipment involved (such as an inverter) are much more expensive and the setup a bit more complex. Most do-it-yourselfers don’t feel the cost-benefit equation works out in favor of AC motors.

If my budget would allow it, I’d use an AC motor. But it doesn’t, so I won’t. I hatched a plan a few weeks ago with the guys at The Electric Car Company of Utah to buy and mount a used DC motor, but after rolling my Bug into the shop and getting a closer look at things, it doesn’t look like that plan will work out.

I met shop owner Carl Clark through Kyle Dansie, who has a couple of homebuilt EVs and introduced me to the Utah EV Interest Group. The EV conversion crowd is full of interesting characters, and Carl is no exception. He is in his mid-70s, and in his many years has been the CEO of a big computer company, started and left several businesses and even served in the Utah state senate. He’s incredibly energetic and engaged, and he told me he believes everything is urgent because he has limited time left to accomplish his goals. He’s running full-steam ahead when most guys his age I know would be playing golf and soaking up sun in Florida.

I told Carl and his grandson, Spencer, who works with him, about my plan to build an EV on a miniscule budget. Carl mentioned he had some slightly used motors he needed to unload and I could get one cheap. Perfect! He offered me a TransWarp 9 from NetGain, which has an excellent reputation among EV gearheads. NetGain makes a motor called a Warp 9, and it’s one of the most popular for conversions. The TransWarp is identical, except that it has a large splined main shaft designed to accept a U-Joint so you can connect it directly to a driveshaft or wheel. The splined shaft won’t work in my Bug, but that’s OK because the TransWarp has another shaft sticking out of the opposite end.

Looks pretty, doesn't it? Too bad it won't work.

After talking it over, we thought we could make the motor work by using the back side shaft, reversing the motor direction (a relatively easy operation) and cutting off the splined main shaft. I was excited because I had found a great motor for almost half of what it would cost me new, and they would help me with the modifications and install.

But after getting a good look at my Beetle, Carl called me with some serious concerns, which Spencer confirmed. First, the motor is too long to fit in the car. I’ve seen some Bug conversions where people have cut a slot in the rear to make the motor fit. Some even have the motor completely exposed in the back, Baja-bug stile. I even thought about mounting a propeller on the shaft sticking out the back end — just for looks, of course. Can you imagine the double takes? But I would prefer to keep my Bug intact.

The real deal-breaker was that the mounting holes on the motor weren’t really ideal. I could go into a long explanation of how the motor mounts to a plate that mounts to the transmission, but suffice to say the TransWarp wasn’t going to work without some serious jury-rigging. Yeah, I could do it, but the added expense would negate the deal I would have gotten on the motor. On to Plan B.

So far, I have two leads:

Carl just got two new motors from Mars Electric. The company has built small motors for awhile now and is trying to get into the full-sized motor market. They sent Carl a couple to try out and cut him a deal. Carl said he’d pass the savings on to me if I want one.

I also spotted an Advanced DC motor on eBay. They’re commonly found under the hoods of homebuilt EVs, and the price is pretty good. Of course, bidding could go through the roof by the time the auction closes after my deadline for this post, so we’ll see what happens.

I’ve also been talking to Brian Berrett of Wilderness EV to get everything I’ll need to mount the motor in my Bug. Looks like he and local EV nut Ralf Finlinson (the guy who sold me my Bug) will be helping me out, and with any luck the motor will be mounted sometime next week. Stay tuned.

Got any advice, suggestions or ideas for Matthew? Share ’em with us! Follow his progress on Twitter @Wired_EV and here at Wired.com every week. He’s also launched a blog, evBeetle.com, to cover the conversion in microscopic detail.

Here’s The Thing With Ad Blockers

We get it: Ads aren’t what you’re here for. But ads help us keep the lights on. So, add us to your ad blocker’s whitelist or pay $1 per week for an ad-free version of WIRED. Either way, you are supporting our journalism. We’d really appreciate it.